Rich Dublin pub starter: thick sourdough toast topped with a bubbling savory sauce of mature Irish Cheddar, dark rich Guinness stout, English mustard, and Worcestershire sauce, grilled until blistered.
Melt butter in a saucepan, whisk in flour for 1 minute, then gradually pour in Guinness stout, whisking until smooth and thick.
Stir in grated Irish Cheddar, mustard powder, Worcestershire sauce, and black pepper over low heat until a thick, spreadable paste forms. Cool slightly.
Toast bread slices under a hot grill on both sides until lightly browned.
Spread Guinness cheese mixture thickly over toast right to edges. Grill under high heat for 3-4 minutes until bubbling, blistered, and golden-brown.